The invention relates to a ceramic heater-type glow plug that is used to assist in starting of a diesel engine.
A ceramic heater-type glow plug that is used to assist in starting of a diesel engine typically has a structure of holding a rear end side of a ceramic heater in a metallic outer cylinder in a state where a heat generating section on a tip side of the ceramic heater is projected to the outside. In such a ceramic heater-type glow plug, a rear end side of the outer cylinder is inserted in and fixed to a tip of a cylindrical housing that is a mounting fixture to a cylinder head of the engine.
In general, manufacturing cost of the ceramic heater-type glow plug heavily depends on length of a ceramic portion. Thus, for a purpose of cutting the manufacturing cost by reducing the length of the ceramic portion, as depicted in FIG. 3, a ceramic heater-type glow plug 300 has practically been used, the ceramic heater-type glow plug 300 having such a structure that one electrode (a negative electrode) 312 of a ceramic heater 310 is exposed on an outer surface of a ceramic insulating substrate 311 and is electrically connected to an inner surface of an outer cylinder 320 and that the other electrode (a positive electrode) 313 is exposed to the outside of the outer cylinder 320 from a rear end thereof via an electrode exposing tool 330 and an electrode exposing rod 340. More specifically, the electrode that has been exposed to the outside of the outer cylinder 320 by the electrode exposing tool 330 and the electrode exposing rod 340 is electrically connected to an external connection terminal 360 that is fixed on a rear end side of a housing 350 via an insulator 370 (for example, see Japanese Patent No. 4,172,486).
Here, the electrode exposing tool 330 that includes a relatively thin lead wire is used in the ceramic heater-type glow plug 300 as disclosed in Japanese Patent No. 4,172,486. Thus, a temperature of the electrode exposing tool 330 may substantially exceed an upper temperature limit thereof. For this reason, the outer cylinder 320 is filled with insulating ceramic power 380, heat of the electrode exposing tool 330 is dissipated via the ceramic power 380, and a temperature increase of the electrode exposing tool 330 is thereby suppressed.